1. Field of the Invention
The present invention relates to a process for preparing a hydrophilic polymer film and particularly, to a process for the preparation of hydrophilic polymer film, which comprises modifying polymer film by coating a photopolymerization solution containing a hydrophilic monomer of low water swelling ability and an UV stabilizer on the film surface pre-treated with a high frequency, and photopolymerizing the solution so as to improve a hydrophilic property, a climate-resistibility, and a blocking property.
2. Description of the Prior Art
Generally, polyolefin films have been widely used in agricultural fields and packing materials fields because of their good mechanical properties, optical property, nontoxic property, and durable flexibility. However, since such conventional films have hydrophobic properties on the surface thereof, the transparency of such conventional films is significantly reduced by condensation of moisture on the inner surface thereof when used in a simple green house built from such polymer films, due to the reduction of the sunlight transmittance through such films.
As a result, the crop of vegetables in the simple green house is reduced and the period of harvest takes a long time. Also, the temperature effect in the green house is reduced. If drops of water condensed on the surface of such films come down on the flower of a crop cultivated in the green house, the crop withers or does not bear fruit.
Due to the hydrophobic property of the film surface, coating materials such as water soluble ink, gelatin, and so on are difficult to coat on the surface thereof. When such films are used for packaging material of foods, the food may become spoiled or decayed due to the drops of water formed in the packaged film surface.
In order to avoid the above problems, and to make the use of polyolefin films more practical, the film surface has been modified as follows.
For example, there is a method for preparing a hydrophilic film by compounding polyethylene resin and a special surfactant, and a method for modifying the polyethylene film by coating a special surfactant on the surface thereof.
However, since the surfactant used on the film is washed away easily by drops of water, the hydrophilic property of the such films can be reduced.
Recently, there has been developed a method of modifying such films by grafting a hydrophilic material on polyethylene film. The film modified by this method continuously maintains the hydrophilic property. But discoloration of the film may occur since the climate-resistibility is not good, and a blocking phenomena sticking between the films occurs on the film surface because of the use of hydrophilic substances having a high water swelling ability such as acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-hydroxyethylmethacrylate, and N-vinylpyrrolidone.